Electric pump

ABSTRACT

An electric pump may comprise a pump case ( 110, 150 ) having a pump chamber. An impeller  143  may be rotatably disposed within the pump chamber. The impeller  143  may include a magnetized cylindrical portion  145 . A stator  133  may be disposed opposite to the cylindrical portion  145  of the impeller  143 . The stator  133  may drive the impeller  143  by applying magnetic forces to the cylindrical portion  145  of the impeller  143 . A shaft  146  may be formed integrally with the impeller  143 . One end of the shaft  143  may be rotatably supported with respect to the pump case.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application numbers 2006-22284, filed on 31 January with the JPO, the contents of which are hereby incorporated by reference into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric pump used to circulate cooling water to cool an automobile engine or an inverter or the like.

2. Description of the Related Art

The known electric pump includes a pump case. A pump chamber is formed in the pump case. An impeller is disposed within the pump chamber. The impeller includes a magnetized cylindrical portion. A bearing is formed integrally in the center of the impeller, and a shaft is inserted into the bearing. One end of the shaft is fixed in the pump casing (in other words, the shaft is supported cantilevered from the pump case). A stator is disposed outside the pump case to drive the impeller. The external peripheral surface of the stator is disposed in opposition to the internal peripheral surface of the cylindrical portion of the impeller. When electrical power is applied to the stator, magnetic forces are generated from the stator to the cylindrical portion of the impeller, as a result of which the impeller rotates. When the impeller rotates a fluid is drawn into the pump chamber via an inlet in the pump case, and the drawn in fluid is expelled from an outlet in the pump case.

However, in this known electric pump, depending on the operating conditions (for example, the output flow rate) or the installation conditions (for example, the installation position of the electric pump), the impeller oscillates about the shaft, and vibrations are generated. In particular, if the member on which the electric pump is installed vibrates (for example, if the electric pump is installed on the body of the engine room of the automobile), the vibrations of the installation member are transmitted to the electric pump, and promote the vibration of the impeller about the shaft. Vibration of the impeller about the shaft causes the problem of unpleasant noise.

SUMMARY OF THE INVENTION

It is an object of the present teachings to provide an electric pump capable of reducing the vibrations of the impeller about the shaft, and controlling the occurrence of unpleasant noise.

In one aspect of the present teachings, an electric pump may comprise a pump case, an impeller, a stator, and a shaft. A pump chamber may be formed within the pump case. The impeller may be rotatably disposed within the pump chamber, and include a magnetized cylindrical portion. The stator may be disposed opposite to the cylindrical portion of the impeller, and drive the impeller by applying magnetic forces to the cylindrical portion of the impeller. The shaft may be fixed to the impeller and rotatably supported with respect to the pump case.

In this electric pump, the shaft is rotatably supported with respect to the pump case, and the shaft is fixed to the impeller. Therefore, there is no relative motion between the impeller and the shaft, and this measure on its own suppresses vibrations of the impeller about the shaft. In other words, in a structure in which the impeller is installed on a shaft fixed to the pump case so that the impeller can rotate with respect to the shaft, there is a clearance between the shaft and the impeller, and the clearance promotes oscillation of the impeller about the shaft. In this electric pump, the impeller is fixed to the shaft, and there is no clearance between the two, so it is possible to suppress vibrations of the impeller about the shaft. In this way, it is possible to suppress the occurrence of unusual sounds.

In another aspect of the present teachings, an electric pump capable of reducing the amount of impeller wear, and improving the impeller durability is provided. In other words, when the impeller is rotating, the fluid drawn into the pump chamber flows in between the impeller and the pump casing. Therefore, the contact force between the impeller and the pump casing is reduced, so impeller wear does not become a problem. However, if air or foreign matter is mixed into the fluid drawn into the pump chamber, the fluid pressure acting on the impeller fluctuates. Therefore, there are occasions when the impeller is strongly forced against pump casing, so impeller wear becomes a problem. If the impeller wears, the durability of the impeller is reduced.

Therefore, an electric pump according to the present teachings may comprise a pump case, a rotation shaft, an impeller, and a stator. A pump chamber may be formed within the pump case. The shaft may be disposed within the pump chamber. A lower end of the shaft may be fixed to the pump case. The impeller may be rotatably disposed within the pump chamber. The impeller may include a magnetized cylindrical portion, and a bearing into which the shaft is inserted. The stator may be disposed opposite to the cylindrical portion of the impeller, and drive the impeller by applying magnetic forces to the cylindrical portion of the impeller. A plurality of grooves may be formed in a lower end surface of the bearing.

In this electric pump, the fluid drawn into the pump chamber can flow in the grooves formed in the lower end surface of the bearing. Therefore, the friction force generated between the bearing of the impeller and the pump casing is reduced. Therefore, wear of the impeller is suppressed, and the durability of the impeller can be improved.

Further, a washer may be disposed between the pump case and the lower end surface of the bearing.

These aspects and features may be utilized singularly or, in combination, in order to make improved electric pump. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or, in combination with the above-described aspect and features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section through an electric pump according to a first representative embodiment;

FIG. 2 is a view showing the bottom surface of the bearing of an electric pump according to the first representative embodiment;

FIG. 3 is a vertical section when viewed from the side of an electric pump according to a second representative embodiment;

FIG. 4 is a plan view of the bearing in an electric pump according to the second representative embodiment; and

FIG. 5 is a plan view showing another example of the bearing in an electric pump according to the second representative embodiment.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

An electric pump 10 according to the first representative embodiment will be explained with reference to the drawings. The electric pump 10 may be used to circulate cooling water to cool the engine of an automobile, and be installed in the engine room of the automobile.

As shown in FIG. 1, the electric pump 10 includes a lower body 12 and an upper body 50 fixed to the lower body 12. Each of the lower body 12 and the upper body 50 may be formed integrally from a material such as resin. A cylindrical shaped protrusion 15 is formed in the top of the lower body 12 (on the left side in the figure). A shaft installation hole 16 a is provided in the center of the protrusion 15. The lower end of a shaft 46 is fixed in the shaft installation hole 16 a. The top end of the shaft 46 projects higher than the top surface of the protrusion 15. An impeller 43 is rotatably attached to the top end of the shaft 46.

An external wall 17 is formed in a cylindrical shape around the protrusion 15. The protrusion 15 and the external wall 17 are disposed concentrically. A circular ring-shaped groove 20 is formed by the protrusion 15 and the external wall 17. A cylindrical portion 45 of the impeller 43 is housed in the groove 20.

A connector 21 is formed in the top of the lower body 12 (the right side in the figure). Electrical wiring 28 is disposed in the connector 21. The lower end of the electrical wiring 28 is connected to terminals 26 on a circuit board 23. The top end of the connector 21 is connected to an external power source that is not shown on the drawings. Electrical power from the external power source is supplied to the circuit board 23 via the electrical wiring 28 and the terminals 26.

The lower end of the upper body 50 may be fixed to the top end of the external wall 17 of the lower body 12. An inlet port 51 and an outlet port (not shown in the drawings) are formed in the upper body 50. The internal space formed by the lower body 12 and the upper body 50 (in other words, the internal space formed by the external wall 17, the protrusion 15, and the upper body 50) functions as the pump chamber. Therefore, the upper body 50 and the lower body 12 correspond to the pump case referred to in the claims.

The pump impeller 43 is disposed within the pump chamber. The impeller 43 may be formed integrally from a synthetic resin, for example a plastic material containing ferrite powder may be used in the manufacture. The impeller 43 may include a substantially circular cylindrical shaped cylindrical portion 45 and a vane portion 44 that closes one end of the cylindrical portion 45. The cylindrical portion 45 may be magnetized by the inclusion of magnetic powder. A plurality of fins may be formed in the vane portion 44.

A bearing 47 is disposed in the center of the vane portion 44. The impeller 43 and the bearing 47 may be formed integrally by insert forming. The bearing 47 may be formed from a poly phenylene sulfide material (PPS material). As shown in FIG. 2, radiating grooves 47 a are formed in the bottom end surface of the bearing 47 (the end surface on the lower body 12 side). The grooves 47 a may extend from the outer peripheral surface of the bearing 47 to a through hole 47 b in the bearing 47.

The shaft 46 is inserted into the through hole 47 b of the bearing 47, so that the impeller 43 can rotate freely about the shaft 46. A washer 52 may be disposed between the bearing 47 and the protrusion 15. A washer 48 may be installed on the top end of the shaft 46 by a screw 49. The impeller 43 is prevented from being lifted up during rotation by the washer 48.

When the impeller 43 is installed on the shaft 46, a clearance is formed between the internal surface of the impeller 43 (internal peripheral surface of the cylindrical portion 45 and the bottom surface of the vane portion 44) and the protrusion 15 of the lower body 12. Also, a clearance is formed between the external peripheral surface of the cylindrical portion 45 of the impeller 43 and the external wall 17 of the lower body 12. Therefore, the cooling water in the pump chamber contacts the surface of the protrusion 15 of the lower body 12 via these clearances.

A board housing portion 14 is formed in the interior of the lower body 12. A stator housing portion 16 is formed in the interior of the protrusion 15. The bottom of the stator housing portion 16 is linked to the board housing portion 14. In this way, a single housing space is formed that houses the circuit board 23. The board housing portion 14 is open at the bottom, so that the circuit board 23 is inserted into the lower body 12 from the bottom of the board housing portion 14. The board housing portion 14 and the stator housing portion 16 are filled with a potting material 41 from a bottom end of the lower body 12. The circuit board 23 is embedded in the potting material 41. In this way, the ingress of liquid from outside into the board housing portion 14 and the stator housing portion 16 is prevented, which prevents erroneous operation and failure of the circuit board 23.

It is preferable that material with a high thermal conductivity is used as the potting material 41. By using a material with a high thermal conductivity, heat from a stator 33 is dissipated to the outside, and the temperature rise of the circuit board 23 can be reduced. Heat conductive silicone, resin, or epoxy type resin may be used as the potting material 41. Furthermore, alumina fibers (filler) may be mixed into the resin. By adding the alumina filler, the thermal conductivity can be increased.

The circuit board 23 includes a board 24 and the stator 33 fixed to the board 24. The stator 33 includes a stator core 34 and a stator coil 35. The stator core 34 may be made by laminating thin steel plates (for example, silicon steel plates) obtained by press forming or similar. A plurality of slots is formed in the stator core 34. A mating hole 34 a is formed in the center of stator core 34. When the stator 33 is housed in the stator housing portion 16, a shaft fixing portion 16 b is fitted to the mating hole 34 a. In this way, the position of the stator 33 within the stator housing portion 16 is fixed to a predetermined position. When the stator 33 is positioned within the stator housing portion 16, the external peripheral surface of the stator 33 is in opposition to the internal peripheral surface of the cylindrical portion 45 of the impeller 43.

The top ends of terminals 37 are fixed to the bottom end of the stator core 34. The bottom ends of the terminals 37 are soldered to a terminal land (not shown on the drawings) of the board 24. In this way, the stator 33 is fixed to the board 24 via the terminal land.

The stator coil 35 is wound around each slot of the stator core 34. One end of the winding wire of the stator coil 35 is connected to the terminal 37.

On the board surface of the board 24 other electronic components (not shown on the drawings) of the stator 33 are mounted and printed wiring (not shown on the drawings) is applied. The electronic components mounted on the board 24 include power elements such as power transistors and power diodes. The power transistors are to switch the electrical power supplied to the stator coil 35, and the power diodes are an element that absorb surge voltages when the power supply is switched.

Also, a temperature sensor 54 is mounted on the board surface of the board 24 via a spacer 56. By inserting the spacer 56, the temperature sensor 54 is disposed in a position close to the stator coil 35. In this way, the temperature sensor 54 can accurately measure the temperature of the stator coil 35 without being affected by the ambient temperature. A thermistor may be used as the temperature sensor 54. A thermistor has the characteristic that as the temperature increases, the electrical resistance reduces. Therefore, the temperature can be measured by the electrical resistance of the thermistor. Apart from a thermistor as described to above, a diode whose electrical characteristics varies with temperature may be used as the temperature sensor 54.

The board 24 may be provided with a shut off circuit (not shown in the drawings) that turns the power transistors OFF when the temperature measured by the temperature sensor 54 exceeds a predetermined value. The shut off circuit may be configured as for example a comparator or the like, that compares the output from the temperature sensor 54 with a predetermined voltage, and turns the output ON or OFF. When the shut off circuit operates, power to the stator coil 35 is shut off to prevent damage to the stator coil 35.

In the electric pump 10 described above, electrical power is supplied in turn to each stator coil 35 of the stator 33 from the circuit board 23. In this way, a magnetic force is generated by each stator coil 35 in turn, these magnetic forces act on the cylindrical portion 45 of the impeller 43, and the impeller 43 rotates. When the impeller 43 rotates, cooling water is drawn into the pump chamber from the inlet port 51. The drawn in cooling water is pressurized by the rotation of the impeller 43, and expelled from the outlet port.

Here, when the impeller 43 rotates, an upward force (uplift force) acts on the impeller 43 from the cooling water within the pump chamber, so the impeller 43 rises up along the protrusion 15 of the lower body 12. As a result, the clearance between the impeller 43 and the protrusion 15 is sufficiently maintained, and cooling water flows into the clearance. In this way, the heat generated by the stator 33 is transmitted to the cooling water within the pump chamber through the wall of the protrusion 15, and the stator 33 is efficiently cooled.

If air is mixed into the cooling water drawn into the pump chamber, the upwards force acting on the impeller 43 is reduced. In the electric pump 10, the washer 52 is disposed between the bearing 47 and the protrusion 15, and radiating grooves 47 a are formed in the bottom surface of the bearing 47. Therefore, even if the upwards force acting on the impeller 43 is reduced, the friction force acting between the bearing 47 and the protrusion 15 is made uniform within the plane by the washer 52. Also, the friction force generated between the bearing 47 and the protrusion 15 is reduced by the cooling water introduced into the radiating grooves 47 a in the bearing 47. In this way, wear of the impeller 43 is reduced, and the durability of the impeller 43 can be improved.

Second Embodiment

Next, the electric pump 100 according to a second representative embodiment is explained. The electric pump 100 may also be used to circulate cooling water to cool the engine of an automobile.

As shown in FIG. 3, the electric pump 100 includes a lower body 110, an upper body 150 fixed to the top end of the lower body 110, and a lid 170 fixed to the bottom end of the lower body 110. A cylindrical shaped protrusion 115 is formed in the top of the lower body 110. An external wall 118 is formed in a cylindrical shape around the protrusion 115. The protrusion 115 and the external wall 118 are disposed concentrically. A cylindrical portion 145 of an impeller 143 is housed between the protrusion 115 and the external wall 118.

A bearing installation hole 117 is provided in the center of the protrusion 115, and a bearing 162 is installed in the bottom of the bearing installation hole 117. A bottom end 146 b of a hollow shaft 146 is inserted into the bearing 162. The bearing 162 supports the bottom end 146 b of the shaft 146. The bearing 162 is a cylindrical shaped member having a bottom, capable of receiving loads from the shaft 146 in the radial direction and the thrust direction. The bearing 162 may be formed from a poly phenylene sulfide material (PPS material) or similar, and be made integral with the lower body 110 by insert forming. The wall forming the bearing installation hole 117 extends downwards beyond the bearing 162, to form a depressed portion 126. A protrusion 172 of the lid 170 is inserted into the depressed portion 126.

As shown in FIG. 4, the bearing 162 includes a shaft installation hole 162 a in the center into which the shaft 146 is inserted, and radial grooves 162 c formed in the surface that contacts the bottom surface of the shaft 146. The grooves 162 c link the clearance between the shaft 146 and the bearing 162 and the hollow portion 144 of the shaft 146, and have the function of facilitating the flow of cooling water between the two. By forming the grooves 162 c, lubrication between the shaft 146 and the bearing 162 can be ensured, and cooling of the stator 133 can be carried out. In other words, by providing the grooves 162 c, the space between the impeller 143 and the protrusion 115 (the spaced formed below the impeller 143) and the space above the impeller 143 are linked by the flow channel formed by the clearance between the external peripheral surface of the shaft 146 and the bearing 162→grooves 162 c →hollow portion 144 of the shaft 146, so cooling water is circulated between the two. Therefore, by increasing the flow rate of cooling water flowing around the protrusion 115 of the lower body 110, cooling of the stator 133 can be effectively carried out. Also, by increasing the flow rate of cooling water flowing in the clearance between the shaft 146 and the bearing 162, the shaft 146 and the bearing 162 can be well lubricated.

As shown in FIG. 5, grooves 162 d may also be formed in the internal peripheral walls of the installation hole 162 a of the bearing 162. By forming grooves 162 d in the internal peripheral walls of the installation hole 162 a, the flow rate of cooling water flowing in the hollow portion 144 of the shaft 146 can be further increased.

A bottom end 158 of the upper body 150 is fixed to a top end 120 of the external wall 118 of the lower body 110. The connection between the top end 120 of the lower body 110 and the bottom end 158 of the upper body 150 may be carried out by laser welding. An inlet port 152 and an outlet port 154 are formed in the upper body 150.

A bearing 160 is disposed in the upper body 150. The bearing 160 supports the top end 146 a of the shaft 146. The bearing 160 can receive loads in the radial direction from the shaft 146. Radial grooves may be formed in the bottom end surface of the bearing 160 (grooves with the same form as the grooves in the bottom end surface of the bearing 47 of the first representative embodiment described above). The bearing 160 may be formed from a poly phenylene sulfide material (PPS material) or similar, and be made integral with the upper body 150 by insert forming.

The impeller 143 is disposed within the pump chamber formed by the lower body 110 and the upper body 150 (in other words, the internal space formed by the external wall 118, the protrusion 115, and the upper body 150). The impeller 143 may be formed integrally from a synthetic resin (for example, a plastic material containing ferrite powder). The impeller 143 includes a substantially circular cylindrical shaped cylindrical portion 145 and a vane portion 144 that closes one end of the cylindrical portion 145. The cylindrical portion 145 is magnetized by the inclusion of magnetic powder. A plurality of fins are provided in the vane portion 144. The shaft 146 is fixed in the center of the vane portion 144. The impeller 143 and the shaft 146 may be formed integrally by insert forming.

When the impeller 143 is housed within the pump chamber, the top end 146 a of the shaft 146 is supported by the bearing 160. The bearing 160 may be made integral with the upper body 150. A washer 156 is disposed between the bearing 160 and the impeller 143. The washer 156 prevents direct contact between the impeller 143 and the bearing 160 when uplift of the impeller 143 occurs due to rotation. In this way, excessive friction forces are prevented from acting on the impeller 143. Also, the grooves provided in the bottom end surface of the bearing 160 also contribute to preventing the occurrence of excessive friction forces between the impeller 143 and the bearing 160.

On the other hand, the bottom end 146 b of the shaft 146 is supported by the bearing 162. The bearing 162 may be made integral with the lower body 110. The bearing 162 can receive loads from the shaft 146 not only in the radial direction, but also in the thrust direction. Therefore, even if air is drawn into the pump chamber while the electric pump 100 is operating and the downwards acting load from the impeller 143 increases, the load acting in the thrust direction can be received by the bearing 162.

Also, when the impeller 143 is disposed within the pump chamber, a clearance (180 c, 180 d) is formed between the internal surface of the impeller 143 (internal peripheral surface of the cylindrical portion 145 and the bottom surface of the vane portion 144) and the protrusion 115 of the lower body 110. Also, a clearance 180 e is formed between the shaft 146 and the protrusion 115 (or more specifically the wall of the bearing installation hole 117). The cooling water in the pump chamber flows through these clearances, so the stator 133 is cooled from the external peripheral surface, the top end surface, and the internal peripheral surface of the stator 133. Therefore, the stator 133 can be efficiently cooled.

The lid 170 is fixed to the bottom end of the lower body 110. The internal space (128 a, 128 b) between the lower body 110 and the lid 170 is preferably sealed. The lower body 110 and the lid 170 may be joined by laser welding all round in order to seal the internal space (128 a, 128 b) between the two. The protrusion 172 is provided in the center of the lid 170. Radiating ribs 174 are provided in the top surface of the lid 170 for strengthening. When the lid 170 is fixed to the lower body 110, the protrusion 172 of the lid 170 is mated within the depressed portion 126 of the lower body 110. In this way, the load of the shaft 146 in the thrust direction can be received by the protrusion 172.

A board 124 is housed within the internal space (128 a, 128 b) enclosed by the lower body 110 and the lid 170. The stator 133 is mounted on the top surface of the board 124. The stator 133 includes a stator core 134 and a stator coil 135. A plurality of slots is formed in the stator core 134, and the stator coil 135 is wound around each slot. A mating hole 134 a is formed in the center of stator core 134. When the board 124 is housed in the lower body 110, part of the bearing installation hole 117 of the protrusion 115 is fitted into the mating hole 134 a. In this way, the stator 133 is located in a predetermined position within the lower body 110. When the stator 133 is installed, the external peripheral surface of the stator 133 is in opposition to the internal peripheral surface of the cylindrical portion 145 of the impeller 143.

Electronic elements such as power transistors and power diodes are disposed on the board 124, similar to the first representative embodiment described above. Also, a choke coil 127 is disposed on the rear surface of the board 124.

The space 128 a above the board 124 is filled with a potting material, and the space 128 b below the board 124 is not filed with a potting material. The reason that only the space 128 a above the board 124 is filled with potting material is to efficiently dissipate heat from the stator 133.

In the electric pump 100 as described above, when the stator 133 is provided with electrical power from the board 124, the impeller 143 rotates due to the magnetic forces from the stator coil 135. When the impeller 143 rotates, cooling water is drawn into the pump chamber from the inlet port 152. The drawn in cooling water is pressurized by the rotation of the impeller 143, and expelled from the outlet port 154.

As is clear from the above explanation, in the electric pump 100 according to the second representative embodiment, even if forces act to cause the impeller 143 to oscillate about the shaft 146 when the impeller 143 rotates, the shaft 146 is integral with the impeller 143, and furthermore both ends of the shaft 146 are supported by the bearings 160, 162. Therefore, vibrations of the impeller 143 about the shaft 146 are suppressed, and the generation of unusual sounds is suppressed. In this way, the durability of the impeller 143 can be improved.

Also, in the present embodiment, the shaft 146 is hollow and grooves 162 c are provided in the bottom surface of the bearing 162, so the cooling water within the pump chamber is positively circulated. Therefore, the flow rate of cooling water around the protrusion 115 of the lower body 110 is large, and cooling of the stator 133 is efficiently carried out.

The electric pump according to each of the representative embodiments described above was an example of outer rotor type electric pump. However, the present teachings may be also applied to an inner rotor type of electric pump.

Finally, although the preferred embodiments have been described in detail, the present embodiments are for illustrative purpose only and not restrictive. It is to be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims. In addition, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above aspects and features. 

1. An electric pump, comprising: a pump case having a pump chamber; an impeller rotatably disposed within the pump chamber, the impeller having a magnetized cylindrical portion; a stator disposed opposite to the cylindrical portion of the impeller, the stator driving the impeller by applying magnetic forces to the cylindrical portion of the impeller; and a shaft fixed to the impeller, wherein the shaft is rotatably supported with respect to the pump case.
 2. The electric pump according to claim 1, further comprising a first bearing for supporting a top end of the shaft and a second bearing for supporting a lower end of the shaft.
 3. The electric pump according to claim 2, wherein the stator is compartmentalized from the impeller by a first wall of the pump case, a first clearance is formed between the first wall and the impeller, and fluid within the pump chamber can flow in the first clearance.
 4. The electric pump according to claim 3, wherein the shaft is disposed penetrating the center of the stator, the shaft is compartmentalized from the stator by a second wall of the pump case, a second clearance is formed between the second wall and the shaft, and fluid within the pump chamber can flow in the second clearance.
 5. The electric pump according to claim 4, wherein the shaft has a hollow portion, and the fluid within the pump chamber can flow in the hollow portion of the shaft.
 6. The electric pump according to claim 5, wherein the second bearing that supports the lower end of the shaft is arranged to receive radial loads and thrust loads.
 7. The electric pump according to claim 6, wherein the impeller and the shaft are formed integrally by insert forming.
 8. An electric pump, comprising: a pump case having a pump chamber; a shaft disposed within the pump chamber, wherein a lower end of the shaft is fixed to the pump case; an impeller rotatably disposed within the pump chamber, the impeller comprising a magnetized cylindrical portion, and a bearing into which the shaft is inserted, wherein a plurality of grooves are formed in a lower end surface of the bearing; and a stator disposed opposite to the cylindrical portion of the impeller, the stator driving the impeller by applying magnetic forces to the cylindrical portion of the impeller.
 9. The electric pump according to claim 8, further comprising a circuit board that provides electrical power to the stator, and a temperature sensor that detects temperature of the stator, wherein the temperature sensor is separated from the circuit board and is disposed in a position close to the stator.
 10. An electric pump, comprising: a pump case having a pump chamber; a shaft disposed within the pump chamber, wherein a lower end of the shaft is fixed to the pump case; an impeller rotatably disposed within the pump chamber, the impeller comprising a magnetized cylindrical portion, and a bearing into which the shaft is inserted; a stator disposed opposite to the cylindrical portion of the impeller, the stator driving the impeller by applying magnetic forces to the cylindrical portion of the impeller; and a washer disposed between the pump case and a lower end surface of the bearing.
 11. The electric pump according to claim 10, further comprising a circuit board that provides electrical power to the stator and a temperature sensor that detects temperature of the stator, wherein the temperature sensor is separated from the circuit board and is disposed in a position close to the stator. 